Thermodynamic properties of actinide complexes. Uranyl(VI)-and thorium(IV)-aspartate systems

Stability constants, enthalpies and entropies in the formation of uranyl(VI) and thorium(IV) with aspartic acid have been determined at 25.00C in a 1.0 mol dm-3 aqueous solution of sodium perchlorate by means of the potentiometric and calorimetric techniques. Because of precipitation of solid compounds, only two complexes of 1:1 and 1:2 stoichiometry were observed in the uranyl(VI)-aspartate system and only one complex of 1:1 stoichiometry in the thorium(IV)-aspartate system. Comparison of values of stability constants and enthalpy and entropy changes with the corresponding values of some mono- and di-carboxylate ligands suggests that the binding of both metal ions involves one carboxylate group only, the one furthest from the positive amino group. (author)